Excel 2016 - open all files in ONE instance

Buying a new version will rarely fix a "bug" like this. Before you spend the money, check to confirm that it really will, otherwise, if you are happy with the older version and it is still supported, save your money.

Hint: you wouldn't be buying 2016 now, you would be buying 2019/365 (unless you buy 2016 from someone other than MS who has "old stock").

Rohn,

Thank you for the reminder to not purchase software on the hope that the feature you need will be there.  I did a quick Google search using "Does excel 2019 support MDI" and arrived at a link:

https://answers.microsoft.com/en-us/msoffice/forum/msoffice\_excel-mso\_other-mso\_o365b/excel-2016-open-all-files-in-one-instance/3792d5ae-3d03-4251-9abd-eb81d64e8fde?page=4&rtAction=1547831502082

Alas, folks there are still grumbling about the lack of MDI support as recently as Jan. 16, 2019.  Most of the comments are from power users who are very much connected to what's happening in Excel.  You can go to the link above and register to receive email updates on the issue. So, my conclusion is NO MDI support in Excel 2019.  Will be sticking with Excel 2010 for some time yet!

I am having the same issue with Office 365 ProPlus 32-bit Excel (Version 1803 Build 9126.2236 Click-to-Run).  I often (but not always) want files opened in a single instance due to some of the reasons already described by other posters: ability to use Paste Special, linking between different files, copying large amounts of data, etc.  The unpredictability of the Open behavior can get frustrating.  Furthermore, since Microsoft removed the saved Workspace functionality (which would bypass the problem altogether), it is doubly annoying.  I do miss Excel 2010.

All that said: I am thinking that the issue may not lie entirely with Excel itself, but rather with File Explorer.  In older version of Windows, it was possible to see, in Explorer Options, the exact command line that each right-click option runs (e.g. Open, New, Print, etc) for individual file extensions and their context.  I am not seeing this option in Windows 10 (specifically Microsoft Windows 10 Enterprise [Version 10.0.16299.904]).

However, in RegEdit, when I go to this registry entry:

Computer\HKEY_CLASSES_ROOT.xlsx

the Default value indicates the file type (presumably) is "Excel.Sheet.12".  With this information in hand, I go to the following registry entry:

Computer\HKEY_CLASSES_ROOT\Excel.Sheet.12\shell\Open

I see this Default entry (path will vary based on where Office is installed):

@C:\Program Files (x86)\Microsoft Office\Root\VFS\ProgramFilesCommonX86\Microsoft Shared\Office16\oregres.dll,-3

If I change this instead to (adjust path to wherever Office is installed):

@C:\Program Files (x86)\Microsoft Office\root\Office16\EXCEL.EXE

and click Open on multiple files (no instances of Excel running), initially in Task Manager it generates a separate instance of Excel for each file, but once the first instance opens, it "merges" (for lack of better word) all the selected files into a single instance.  I've tried this with up to 15 (small) workbooks.

Lamentably, there appears to be a shortfall with this workaround: if an instance of Excel is already running, and you Open the files as described above, they will open in a new instance - but at least it's a single new instance.

Obviously, if the files have different extensions, you would need to do this for each one (e.g. xlsb, xlsm, xls).  Also, I have not tested this extensively - only local files (not synced, not on Windows network), all opening in NOT protected mode and NOT read-only, not Outlook attachment, and not generated by any kind of external application such as an Export function in accounting software.  These situation may warrant further testing.

I realize this does not fully solve OP's issue, but hopefully it is a lead.

Thanks for your work and post RanOtherwise! Looks promising.

yes you will have same issue.  I hate it,  I go to open a work book,  eachtime i open a work book  it starts a new instance of excel.

I wish to point out one more issue with multiple instances of excel.

When we open multiple files in a single instance, the ribbon on top is spread on the entire screen and multiple files are open. It is so easy to work when most of the ribbons are visible in a single screen

But when we open multiple instances, this is how the ribbon looks

It is so cumberome to work in excel when I open 4 files and it opens in four instances.

Q - why do you want them all in the same process?

A - multiple reasons, but here are my top four:

1. to have full copy&paste functionality between workbooks - it's not possible to paste special (values, formulas, etc.) between workbooks open in different instances.
2. to be able to utilize multiple existing macros we've built at work over the years which rely on workbooks being open in the same process, without having to write complex code to account for a possibility of multiple processes.
3. to be able to use macros stored in a macro workbook that's not an add-in on all my open excel files (i.e. with file scattered between multiple instances, trying to open the macro workbook in the consecutive instance triggers a warning that the file is already open and does not
4. similarly to point 2, to be able to easily create simple macros whenever I need to automate a repetitive task, i.e. the below simple example code that I could use in a single instance, will not work if Excel decides to open wb2 in a new process:

Sub test()

Set wb1 = Workbooks("test1.xlsx")

Set wb2 = Workbooks("test2.xlsx")

wb1.Sheets(1).Range("A1:H40").Value = wb2.Sheets(1).Range("A1:H40").Value

End Sub

Thanks for the suggestion re Excel 2010. I obviously would have done it long time ago if Excel 2016 wasn't forced company-wide.

@Rohn007 - would you agree that these are good reasons for wanting the consistency of a single Excel instance? MS messed up the above functionalities by allowing Excel to open in a new instance whenever it feels like it.

@Gloria - how is the investigation progressing?